Polymeric compounds having pendant sulphonate groups for use in a radiation sensitive composition

ABSTRACT

A polymeric compound is derived from a polyhydric material and has pendant sulphonate groups of the general formula ##STR1## where X is an aliphatic, aromatic, carbocylic or heterocyclic group; Y is hydrogen, halogen or an alkyl, aryl, alkoxy, aryloxy or aralkyl group, CO.sub. --Z + , CO 2  R or SO 3  -Z +  ; Z +  is a cationic counter ion and R is hydrogen, alkyl, alkylene, aryl or aralkyl group.

This is a division of U.S. patent application Ser. No. 405,875, filedAug. 30, 1989 now U.S. Pat. No. 5,120,799.

This invention relates to novel polymeric compounds and moreparticularly, but not exclusively, is concerned with such compounds foruse in radiation-sensitive compositions for coatings in printing plateproduction or photoresists.

In use, such radiation sensitive compositions are coated on a suitablesubstrate and image-wise exposed to radiation so that parts of thecomposition are struck by the radiation and parts are not. Theradiation-struck and non-radiation-struck parts have differingsolubilities in developer liquids and thus the more soluble parts can beselectively removed by applications of such a liquid to leave an imageon the substrate constituted by the less soluble parts. Forenvironmental and health reasons there has been an increasing tendencyfor wholly aqueous or substantially aqueous based solutions, rather thanorganic solvents, to be used as the developer liquids. In addition, forenvironmental, health, and practical reasons it is also desirable to useneutral or mildly alkaline developer liquids rather than stronglyalkaline developers. For example where high developer pH is apre-requisite for adequate development, reduction in the pH of thedeveloper can occur rapidly in automatic processors due toneutralization by dissolution of acidic radiation sensitive coatingcomponents and due, particularly, to absorption of carbon dioxide fromthe atmosphere hence rendering the developer inactive or `exhausted`. Itis thus desirable to provide radiation sensitive compositions whichexhibit excellent developability at low coating acidity and whichrequire neutral or only mildly alkaline developers and hence givesignificantly extended developer life. For such solutions to beeffective, the radiation-sensitive compositions must be soluble, or atleast swellable, in such solutions.

It is an object of the present invention to provide a polymeric compoundfor use in the preparation of radiation sensitive compositions of thistype.

According to one aspect of the present invention, there is provided apolymeric compound comprising a plurality of substituent sulphonategroups wherein the polymeric compound is derived from a polyhydricmaterial and wherein the sulphonate groups are selected from groups ofthe general formula ##STR2## where X is an aliphatic, aromatic,carbocyclic or heterocyclic group; Y is hydrogen, halogen, or an alkyl,aryl, alkoxy, aryloxy or aralkyl group, CO₂ -Z⁺, CO₂ R or SO₃ -Z⁺ ; Z⁺is a cationic counter-ion and R is hydrogen, alkyl, alkylene, aryl oraralkyl group. In an embodiment of the invention the sulphonate groupsmay be derived from sulphonato substituted acids of the formula ##STR3##where X, Y, Z⁺ and R have the meanings specified above.

In another embodiment of the invention the sulphonate groups may bederived from a reactive derivative of a carboxylic or sulphonic acid.Suitable derivatives are, for example, acid chlorides or anhydrides.

In another embodiment of the invention the polymeric compound maycomprise two or more different counter-ion species, at least one ofwhich species may be radiation sensitive.

In a further embodiment of the invention, the polymeric compound may beincorporated into a radiation sensitive composition in combination witha diazo compound, a photo-polymerisable compound or a positive workingphoto-solubilising compound.

According to another aspect of the present invention there is provided aprocess for the production of a polymeric compound wherein the processcomprises providing a polyhydric material having hydroxyl groups andreacting the hydroxy groups of a polyhydric material with a sulphonatosubstituted acid of the formula ##STR4## or with an ester formingderivative thereof to obtain the desired polymeric compound whichcomprises substituent sulphonate groups of the general formula ##STR5##where X, Y, Z⁺ and R have the meanings specified in above.

If required, subsequent ion exchange of the initial counter-ion Z⁺ toalternative preferred cations is facilitated within the process eitherdirectly, as part of the polymer isolation procedure, or in a subsequention-exchange treatment of the previously isolated sulphonic acidderivative. This is particularly desirable where the initial counter-ionis H⁺.

In a yet further embodiment of the invention the initial counter-ionspecies may be exchanged for a final desired counter-ion species bymeans of an ion exchange process.

Suitable synthetic polymers containing hydroxy groups include, inparticular, polymers having vinyl alcohol units, such as partiallysaponified polyvinyl esters; polyvinyl acetals having free hydroxygroups and corresponding reaction products derived from copolymershaving vinyl ester units or vinyl acetal units or vinyl alcohol units.Also usable are epoxy resins and saponified epoxy resins, copolymers ofallyl alcohol or higher molecular weight unsaturated alcohols, hydroxyacrylic polymers, for example poly (hydroxyalkyl) (meth) acrylatepolymers, phenolic polymers such as phenol formaldehyde resins and vinylphenol polymers, and other similar polymers.

Optionally, the polymeric material may also contain ester groups derivedfrom aliphatic or aromatic carboxylic acids such as octanoic acid,lauric acid or benzoic acid.

The molecular weights of the polysulphonate compounds of the inventioncan vary over a wide range. Generally, the polysulphonates have averagemolecular weights in the approximate range between 900 and 200,000 andpreferably between 900 and 100,000. The degree of esterification of thepolysulphonate products can be quantified in terms of acid-values (AV)where Z⁺ =H⁺, or `acid-value equivalence` (AVE) where Z⁺ is other thanH⁺, where the acid-value equivalence refers to the acid-value of thepolysulphonate (Z⁺ =H⁺) prior to ion-exchange. The AVs or AVEs of hepolysulphonates vary between 5 and 150, preferably between 10 and 90.

Examples of suitable sulphonato-substituted acids and derivatives are:2-sulphobenzoic acid cyclic anhydride;3,4,5,6-tetrabromo-2-sulphobenzoic acid cyclic anhydride; sulphoaceticacid; 2-sulphobenzoic acid; 4-sulphobenzoic acid, 5-sulphoisophthalicacid; 4-sulpho-1,8-naphthalic anhydride; 3-sulpho-2-naphthoic acid;3-sulphophthalic acid; 4-sulphophthalic acid; 4-sulphobenzoyl chloride;naphthalene-1,5-disulphonyl chloride; naphthalene-2,6-disulphonylchloride; benzene-1,3-disulphonyl chloride;anthraquinone-1,5-disulphonyl chloride; 2-sulphobenzene sulphonic acidcyclic anhydride; 3-sulphonaphthalene-8-sulphonic acid cyclic anhydride;3-sulpho-2-naphthoic acid cyclic anhydride; 3-sulphopropionic acidcyclic anhydride; furan-2-chlorocarbonyl-5-sulphonic acid; and2-sulphohexadecanoic acid, 2-sulpholauric acid, 2-sulphomyristic acid,2-sulphostearic acid, 2-sulphobehenic acid and their cyclic anhydrides.

A wide range of cationic species may be employed, either individually orin combination, as the counter-ions of the poly sulphonate compounds ofthe invention and, as such, this allows flexibility to obtainpolysulphonate compounds having the required coating solubility and therequired radiation-sensitive composition characteristics of, for examplesensitivity, hydrophobicity, oleophilicity, developability, image colourcontrast, stability, developer life and press performance.

For example, such properties can be improved by selecting the cationsfrom:

A) Cations which have an active role in the essentialradiochemical/photochemical reaction on exposure of the composition toradiation, for example as a photosensitiser, photoinitiator,photoactivator, photocrosslinking agent, photoactive acid-release orbase-release compound, photooxidant and photo solubilisation agent.

B) Cations which have an active role in a radiation induced reactionwhich results in the generation of solubility differentials, for exampleas a cleavable compound, solubilisable compound, a crosslinkablecompound, a polymerisable component, or which results in the productionof a colour change, for example as indicators, dyes, dye precursors andcolour formers.

C) Cations which have the role of introducing desired performancecharacteristics into the radiation-sensitive composition, for example,polymers, colourants, inhibitors, stabilisers, adhesion promoters,activators, catalysts, surfactants, development aids, oleophilicityenhancers and such like.

Cations may be used individually or in combination to provide thedesired radiation sensitive composition characteristics.

Examples of suitable cations which may be used are:

i) Hydrogen

ii) Metals such as sodium, potassium, lithium, magnesium, calcium andsilver

iii) Quaternary ammonium compounds such as ammonium (N⁺ H₄),5-benzylthiuronium, trimethylglycidyl ammonium, vinylbenzyltrimethylammonium, dimethyldiallyl ammonium, benzylmethyldiallyl ammonium,trimethyl ammonium ethylmethacrylate, 4-azidophenyldiethyl ammonium,4-benzoylbenzyl-trimethyl ammonium,3-(9-oxo-9H-thioxanthen-2,3-α-4-yloxy)-N,N,N-trimethyl-1-propanaminium,benzyldimethyldodecyl ammonium, benzyldimethylhexadecyl ammonium,benzyldimethyltetradecyl ammonium, benzyltributyl ammonium,benzyltriethyl ammonium, benzyltrimethyl ammonium dodecylethyldimethylammonium, ethylhexadecylmethyl ammonium, hexadecYltrimethyl ammonium,methyltrioctyl ammonium, octadecyltrimethyl ammonium, phenyltrimethylammonium, tetrabutyl ammonium, tetradecyltrimethyl ammonium,tetradodecyl ammonium, tetraethyl ammonium, tetraheptyl ammonium,trioctyl ammonium, triethyl ammonium, benzyl amaonium, benzyldimethylammonium, hydroxymethylisopropyl ammonium,didodecylmethylethylmethacrylate ammonium, tetrahexyl ammonium,tetramethyl ammonium, tetraoctadecyl ammonium, tetraoctyl ammonium,tetrapentyl ammonium, tetrapropyl ammonium, tributylheptyl ammonium andtributylmethyl ammonium.

iv) Quaternary-N-heterocyclic compounds such asN-methyl-N-vinylpyridinium, N-hexadecylpyridinium, N-methylquinolinium,N-methylbenzothiazolium, N,4,4-trimethyl-2-oxazolinium,N-methylphenazonium, 4-dimethylaminostyryl pyridinium, and2-azidobenzimidazolium, pyridinium, piperidinium and morpholinium.

v) Diazo Compounds such as 4-diazodiphenylamine, 4-diazodiphenylaminepolycondensates, compounds as disclosed in EP-A 0 233 072, compounds asdisclosed in EP-A 0 030 862, and 2,5-diethoxy,4-(4'methylphenyl)benzenediazonium.

vi) Polymeric compounds such as poly

co(vinylpyrrolidone/vinylimidazolium), poly(5-vinyl-1,2,-dimethylpyridinium), poly (4-vinyl-1-methylpyridinium),and poly(2[4'methoxystyryl-] methylpyridinium).

vii) Cationic dyes such as 3,3'-Diethyloxacarbocyanine, Crystal Violet,Malachite Green, Acridine Orange, and Rhodamine 6G.

viii) Other Compounds such as triphenylcarbenium,2,4,6-tritolylpyrylium, 2-carboethoxy-4,6-diphenylpyrylium,2-methyl-3-phenylbenzopyrylium, trimethylsulphonium,trimethylsulphoxonium, triphenylsulphonium, diphenyl iodonium, dithienyliodonium, 2,4,6-triphenyltriapyrylium, 2,5-dimethylbenzdithylium,triphenyl selenonium, n-hexadecyltri-n-butylphosphonium, allyltriphenylphosphonium, cinnamyltriphenyl phosphonium, 9-fluorenyl phosphonium,benzyltriphenyl phosphonium and 4-benzoylbenzyldimethyl phosphonium.

The above examples represent a small proportion of the cations which maybe used as counter-ions for the polysulphonate compounds of theinvention. Reference may be made to Review of Light-SensitiveTetraarylborates by Douglas G. Borden from Photographic Science andEngineering, Vol.16, Number 4, July-August 1972 which furtherillustrates the range of classes of cations suitable for use.

The reactions between the synthetic polymer containing hydroxy groupsand the sulphonato substituted organic carboxylic acid, acid chloride oracid anhydride or the sulphonato substituted organic sulphonic acid,acid chloride or acid anyhydride are readily achieved and provide veryefficient and reproducible esterification processes. This enablespolysulphonates of required acid values for particular applications tobe prepared readily. Mixed carboxy/sulphonate acids or reactive acidderivatives thereof react with synthetic hydroxy containing polymers toform the corresponding carboxy esters. Evidence of this specificity ofreaction is provided by V Iyer and N K Mathur; Anal. Chim. Acta., 554,33, 1965 (2-sulphobenzoic acid cyclic anhydride) and EE Gilbert,`Sulphonation and Related Compounds`, Chapter 5, J Wiley, Interscience,1965.

The esterification reactions can be carried out in a range of organicsolvents for example N-methylpyrrolidone, butanone, tetrahydrofuran,dioxane or other ethers. Basic catalysts, for example tertiary amines orsodium carbonate are generally employed. Alternatively, esterificationsundertaken with acid derivatives other than the acid chloride or acidanhydride may be effected with catalysts such asdicyclohexylcarbodiimide.

Ion-exchange reactions can be carried out by a number of methods knownto those skilled in the art. Preferred examples include; i) addition ofa reagent which provides cation Z⁺ in the final polysulphonate to theesterification reaction liquors, optionally followed by drown out ofthose liquors into water, ii) drown out of the esterification liquorsinto liquors containing a reagent which provides cation Z⁺, and iii)dispersion of a reagent which provides cation Z⁺ in a preferred coatingsolvent followed by addition of the isolated polysulphonate compoundwith resultant dissolution of the polysulphonate compound after a periodof agitation of the coating liquors.

The compounds of the invention may be incorporated into a variety ofradiation sensitive compositions, well known to those skilled in the artand detailed in `Chemistry for the Graphic Arts` by Paul J. Hartsuch andin `Light Sensitive Systems` by Jaromir Kosar. In this case, thepolysulphonate may be used in simple admixture with the components ofthe radiation-sensitive composition. In such an application, the primaryrole of the polysulphonate is that, described by those skilled in theart, of a `binder` resin or a `support` resin. Such resins have twoprincipal functions, one of which is to increase the durability andresilience of the composition, which is particularly desirable inprinting applications where extended press runs are required, and theother is to provide suitable development properties in preferreddeveloper compositions. Preferred examples of the use of thepolysulphonates as binder resins in radiation sensitive compositionsare; in combination with diazo compounds; photopolymerisable compounds,for example containing acrylate oligomers; positive-working,photosolubilisable compounds, for example, quinone diazide compounds orquinone diazide polymers said polymers containing both sulphonate groupsand quinone diazide groups, the latter linked to the polymer through asulphonate ester linkage, and such like. As indicated previously, thecomposition of the compounds of the invention may be designed andselected to impart additionally desired properties to theradiation-sensitive composition such as hydrophobicity, sensitivity,stability and such like. The proportion of polysulphonate compoundemployed in such radiation sensitive compositions can vary between widelimits depending on the nature of the composition and will generally befrom 95 to 5, preferably from 90 to 25, percent by weight of the totalcoating components.

Alternatively, however, it is also possible to provide radiationsensitive compositions in which radiation sensitive components areintroduced, either fully or in part, by using a radiation-sensitivecation, for example, diazo N₂ ⁺, azido-quaternary ammonium compounds,cationic cyanine sensitiser dyes, cationic photoinitiators and such likeas the counterion species of the polysulphonate of the invention asindicated previously (cation group A).

The radiation sensitive compositions of the present invention may alsocontain additional components known to those skilled in the art tofurther improve performance, for example dyes, pigments, stabilisers,fillers, surfactants, plasticizers, adhesion promoters and also otherresins or polymers.

The following examples illustrate the invention:

EXAMPLE 1

52.8 Parts by weight of a poly (vinyl butyral) comprising 71wt% vinylbutyral units, 26wt% vinyl alcohol units and 3wt% vinyl acetate units,and having weight average molecular weight of about 15,000-17,000, wasdissolved in 600 parts by weight of 1-methyl-2-pyrrolidone by heating to40° C. On cooling to 25° C., 44.2 parts by weight of 2-sulphobenzoicacid cyclic anhydride and 2.5 parts by weight of sodium carbonate werethen added, and the mixture was maintained for 3 hours at 25° C., whilestirring. After cooling to 20° C. the clear solution formed was pouredinto 10,000 parts by weight of a 5% aqueous solution ofbenzyldimethyltetradecyl ammonium chloride.

The resultant white solid polysulphonate compound was collected on afilter, washed with water and dried in vacuo to constant weight. The AVEof the product was 46, and the yield was 70 parts by weight.

EXAMPLE 2 Stage 1

52.8 Parts by weight of the poly (vinyl butyral) described in Example 1was mixed with 33.1 parts by weight of 2-sulphobenzoic acid cyclicanhydride, 1.9 parts by weight of sodium carbonate and 600 parts byweight of 1-methyl-2-pyrrolidone and maintained at 25° C. for 4 hours.After cooling to 20° C. the clear polysulphonate solution was dilutedwith 6,000 parts by weight of water.

Stage 2 2a) Urethane Preparation

P-(N-ethyl-N-2-hydroxyethyl) amino acetanilide (2 mole) in 1-methyl2-pyrrolidone was added to a solution of 2,4-toluene diisocyanate (1mole) in 1-methyl 2-pyrrolidone at room temperature. Dibutyl tindilaurate was added as catalyst and the mixture was heated to 50° C. forfive hours, cooled and dripped into water with vigorous stirring. Theresulting precipitate was filtered off and washed with water.

2b) Hydrolysis of Acetylamino Groups

The damp Stage 2a product was mixed with 6N hydrochloric acid andrefluxed for 2 hours. The resulting solution was neutralised with sodiumhydroxide and the resulting precipitate washed with water and dried.

2c) Diazotisation of Amino Groups

The Stage 2b produce (1 mole) was added to 6N hydrochloric acid and themixture cooled to 5° C. Sodium nitrite solution (1.05 mole) wasintroduced dropwise, the temperature being maintained below 10° C. untildiazotisation was complete.

Stage 3

The solution from stage 2c was mixed with the solution obtained in Stage1 and the product isolated by filtration.

EXAMPLE 3

60 Parts by weight of the poly (vinyl butyral) described in Example 1was dissolved in 300 parts by weight of 1-methyl-2-pyrrolidone. 19.3parts by weight of 2-sulphobenzoic acid cyclic anhydride and 1.2 partsby weight of sodium carbonate were then added and the mixture wasstirred at 25° C. for 2.5 hours. The clear solution formed was thenpoured dropwise into 10,000 parts by weight of water to yield a whiteprecipitate which was collected on a filter, washed with water and driedin vacuo to constant weight (yield 54 parts by weight). Analysis: free2-sulphobenzoic acid 0.3%w/w, AV 28.6.

EXAMPLE 4

60 Parts by weight of the polysulphonate of Example 3 was dissolved in300 parts by weight of α 1:9 1-methyl-2-pyrrolidone:ethanol mixture towhich 15 parts by weight of benzyldimethyltetradecyl ammonium chloridewas added. The resulting clear solution formed was then poured dropwiseinto 10,000 parts by weight of water and the resultant solid collectedon a filter, washed with water and dried in vacuo to constant weight(Yield 61 parts by weight). Analysis showed polymer bound counter-ion tobe 18.4%w/w and free counter-ion to be less than 0.1%w/w.

EXAMPLES 5-16

The procedure of Example 3 was repeated using 28 parts by weight of2-sulphobenzoic acid cyclic anhydride to provide a polysulphonate offree-acid content less than 0.1%w/w and an AV of 38.4. This resin wasused to produce a range of samples with alternative counter-ions, asindicated below, using a similar procedure to Example 4.

    ______________________________________                                        EXAMPLE   COUNTER-ION                                                         ______________________________________                                         5        Benzyltrimethyl ammonium chloride                                    6        Benzyltriethyl ammonium chloride                                     7        Acetonyltriphenyl phosphonium                                        8        Benzyldimethylhexadecyl ammonium chloride                            9        Glycidyltrimethyl ammonium chloride                                 10        Timethylammoniumethylmethacrylate                                   11        3,6-Diamino-10-methylacridinium                                     12        3-(9-oxo-9H-Thioxanthen-2,3-γ-4-                                        yloxytrimethyl)-propanaminium                                       13        3,3-Diethyloxacarbocyaninium                                        14        Basic Violet 11:1                                                   15        Basic Blue 7                                                        16        Sodium                                                              ______________________________________                                    

EXAMPLE 17

60 Parts by weight of an epichlorohydrin Bisphenol-A condensate with OHequivalent weight of 8.04 g (0.47 mol)/100g was dissolved in 600 partsby weight of 1-methyl-2-pyrrolidone at 25° C. 2.6 Parts by weight of2-sulphobenzoic acid cyclic anhydride and 0.15 parts by weight of sodiumcarbonate were then added and the mixture was stirred at 25° C. for 2hours. A water soluble product was formed which was isolated by pouringinto 10,000 parts by weight of a 5% aqueous solution ofbenzyldimethyltetradecyl ammonium chloride. The resultant white solidpolysulphonate compound was collected on a filter, washed with water anddried in vacuo to constant weight. Yield 52.5 parts by weight.

EXAMPLE 18

60 Parts by weight of cresol novolak resin was dissolved in 600 parts byweight of methyl ethyl ketone at 30° C. 38.6 parts by weight of2-sulphobenzoic acid cyclic anhydride and 2.3 parts by weight of sodiumcarbonate were then added, on which the mixture turned dark red. Afterstirring at 30° C. for 2 hours, most of the solvent was removed and theproduct isolated by pouring into 6,000 parts by weight water. Afterfiltering, washing and drying in vacuo, 50 parts by weight of a finepowder product was obtained which had an AV of 132.

EXAMPLE 19

60 Parts by weight of a poly (vinyl formal) comprising 82wt% vinylbutyral units, 12wt% vinyl acetate units and 6wt% vinyl alcohol units,and having weight average molecular weight of about 10,000 to 15,000 wasdissolved in 300 parts by weight of 1-methyl-2-pyrrolidone. 14.34 partsby weight of 2-sulphobenzoic acid cyclic anhydride and 0.09 parts byweight of sodium carbonate were then added, and the mixture was stirredat 35° C. The clear solution formed was poured into 10,000 parts byweight of water and the precipitate formed was washed and dried in vacuoto yield 52 parts by weight of a fine white powder. This on analysis wasfound to have free monomeric acid content of less than 0.1%w/w and AV10.1.

Ion exchange was carried out as described in Example 4 to provide thebenzyldimethyltetradecyl ammonium salt of the polysulphonate.

EXAMPLE 20

The procedure described in Example 3 was used to modify 60 parts byweight of a poly (vinyl butyral) comprising 71 wt % vinyl butyral units,26 wt % vinyl alcohol units and 3 wt % vinyl acetate units and havingweight average molecular weight of 45,000 to 50,000. The addition of16.2 parts by weight 2-sulphobenzoic acid and 0.9 parts by weight sodiumcarbonate yielded a product with free acid content 0.1%w/w and AV 28.05.Ion-exchange using benzyldimethyltetradecyl ammonium chloride wasundertaken as in Example 4.

EXAMPLE 21

The procedures described in Examples 18 and 4 were repeated using astyrene/allyl alcohol co-polymer of molecular weight 2,500 and 5-7% byweight hydroxyl groups as the hydroxy containing synthetic polymer. Theproduct had an AVE of 14.3.

EXAMPLE 22

The procedure described in Example 1 was repeated using apolyvinylbutyral comprising 46 mole % vinylbutyral units, 2 mole %vinylacetate units, 42 mole % vinyl alcohol units and 10 mole % vinyloctanoate units. The product had an AVE of 32.3.

EXAMPLE 23

The procedure described in Example 1 was repeated using Macrynal SM 548,a hydroxy acrylic copolymer of hydroxy value 66, after evaporation ofxylene/butyl acetate solvents. The product had an AVE of 19.4.

EXAMPLE 24

The procedure in Example 1 was repeated using DP 6-3095 hydroxyacrylicpolymer (Allied Colloids) of hydroxy value 155. The product had an AVEof 35.2.

EXAMPLES 25 TO 30

The procedure of Example 1 was repeated except in the selection ofesterification agent and reaction conditions. Polysulphonates wereprepared as indicated in the following table:

    __________________________________________________________________________    Example              Charge of   Reaction                                                                            AEV of                                 No   Esterification Agent (EA)                                                                     EA/p.b.w.                                                                           Catalyst                                                                            Temp/°C.                                                                     Product                                __________________________________________________________________________    25   4-Sulpho-1,8-naphthalic                                                                       66.8  Na.sub.2 CO.sub.3                                                                   60    51.4                                        anhydride                                                                26   4-Sulpho benzoyl chloride                                                                     53.0  Pyridine &                                                                          20    38.4                                                              DMAP                                               27   3,4,5,6-Tetrabromo-2-sulpho-                                                                  120.1 Na.sub.2 CO.sub.3                                                                   25    20.1                                        benzoic acid cyclic anhydride                                            28   3-Sulphopropionic acid                                                                        32.7  Na.sub.2 CO.sub.3                                                                   35    41.0                                        cyclic anhydride                                                         29   Furan-2-chloro carbonyl-5                                                                     48.6  Pyridine &                                                                          20    34.2                                        sulphonic acid        DMAP                                               30   Benzene-1,3-disulphonylchloride                                                               73.7  Pyridine &                                                                           5    29.4                                                              DMAP                                               __________________________________________________________________________     DMAP = Dimethylaminopyridine                                             

EXAMPLE 31

A solution in ethylene glycol monomethyl ether comprising:

2 parts by weight of the polymer of Example 1,

1 part by weight of the diazo compound (41) described in EP-A 0 030 862,and

0.1 parts by weight of Victoria Blue B was whirler coated onto a sheetof electrochemically

grained and anodised aluminium and dried to form a radiation sensitiveplate (A). The coating weight was 0.8 gm⁻².

A second radiation sensitive plate (B) was made in the same way, exceptthat a polymer derived from the same grade of poly (vinyl butyral) asused in Example 1 and modified with phthalic anhydride, as described inExample 5 of U.S. Pat. No.4631245, but having an AV of 60, was usedinstead of the polymer of Example 1.

Plate (A) was exposed through a continuous tone Stouffer stepwedge to UVlight (450 mJcm⁻² from a Berkey-Ascor printing down frame) and developedwith an aqueous neutral pH solution containing 8% anionic surfactant.The developed image of the printing plate had a stepwedge of solid 4,tail 10.

The developed image had good ink receptivity and when the plate wasplaced on a proofing press, the image became fully charged with inkafter only 4 passes of the inking rollers.

Plate (B) was exposed in the same way but failed to develop using theabove developer and required an alkaline (pH11) developer containingtrisodium phosphate. When placed on a proofing press, 12 passes of theinking rollers were required for the image to become fully charged.

EXAMPLE 32

Example 31 was repeated except that 1 part by weight of the condensationproduct of 4-diazodiphenylamine and formaldehyde was used as theradiation sensitive compound in place of diazo compound 41 of EP-A 0 030862. Similar results were obtained.

EXAMPLE 33

A solution in ethylene glycol monomethyl ether comprising:

3 parts by weight of the polymer of Example 2, and

0.1 parts by weight Victoria Blue B was whirler coated onto a sheet ofelectrochemically grained and anodised aluminium and dried to form aradiation sensitive plate. The coating weight was 0.8 gm⁻².

The radiation sensitive plate was exposed through a continuous toneStouffer step wedge to UV light (450 mJcm⁻² from a Berkey-Ascor printingdown frame) and developed with an aqueous neutral pH solution containing10% anionic surfactant and 5% benzyl alcohol.

The developed image of the printing plate had excellent ink receiptivityand a step wedge reading of solid 4, tail 11.

EXAMPLE 34

A solution in ethylene glycol monomethyl ether comprising:

2.7 parts by weight of the diazo compound (41) described in EP-A 0 030862,

1 part by weight of the polymer of Example 1, and

0.25 parts by weight of Basic Red (CI45160)

was whirler coated onto a sheet of electrochemically

grained and anodised aluminium and dried to form a radiation sensitiveplate. The coating weight was 0.6 gm⁻².

The plate was exposed as described in Example 31, except that anexposure of 600 mJcm⁻² was used, and was developed with an aqueousneutral pH solution containing 10% anionic surfactant. The developedimage of the plate had a step wedge reading of solid 4, tail 10 and astrong red image colour.

The developed image had good ink receptivity and when the plate wasplaced on a proofing press, the image became fully charged with inkafter only 5 passes of the inking rollers.

A similar plate containing, as the binder, the polymer derived from poly(vinyl butyral) and phthalic anhydride, as described in Example 31,instead of the polysulphonate of the present invention, required anexposure of 900 mJcm⁻² and also the use of an alkaline developer similarto that described for plate B in Example 31 to give the same step wedgereading. The plate also gave a weak coloured image and evidence ofconsiderable dye leaching during development. When placed on a proofingpress this plate required 14 passes of the inking rollers to fullycharge the image with ink.

EXAMPLE 35

Example 34 was repeated except that the diazo compound was replaced bythe same weight of the condensation product of 4-diazodiphenylamine andformaldehyde.

Similar results were obtained.

EXAMPLE 36

A solution in ethylene glycol monomethyl ether comprising:

2 parts by weight of the polymer of Example 1,

1 part by weight of the diazo compound (41) described in EP-A-0 030 862,and

0.3 parts by weight of Microlith Green GT predispersed pigment

was whirler coated onto a sheet of electrochemically grained andanodised aluminium and dried to form a radiation sensitive plate. Thecoating weight was 0.85 gm⁻².

The plate was exposed and developed as described for Plate A in Example31. The developed image of the plate had a strong colour, excellent inkreceptivity, and a stepwedge reading of solid 5, tail 9.

A similar plate but containing, as the binder, the corresponding polymerderived from poly (vinyl butyral) and phthalic anhydride, as describedin Example 31, instead of the polysulphonate of the invention, had avery weak colour strength and poor coating appearance indicating thatthe binder resin was unable to support adequate pigment dispersion. Thedevelopment properties of this plate were similar to Plate B of Example31.

EXAMPLE 37

Example 36 was repeated using the following alternative comments:

2 parts by weight of the polymer of Example 1,

1 part by weight of the diazo compound described in EP 0233072,-(Example4), and

0.3 parts by weight of Microlith Blue 4GK predispersed pigment.

This formulation also provided a plate of excellent image colour, inkreceptivity and developability.

EXAMPLE 38

The polysulphonate of Example 4 and a polycarboxylic acid of AV 28.3(Resin A), derived by phthalic anhydride modification of the same gradeof poly (vinyl butyral) were used to prepare radiation-sensitive platesas described in Example 31. The development properties of the 2 plateswere compared using the following developers:

    ______________________________________                                                       Developer Composition                                                         Surfactant                                                     Developer pH         Type      Level %                                        ______________________________________                                        A         7.5        Anionic   10                                                                  Non-Ionic 15                                             B         7.7        Anionic   28                                                                  Non-Ionic  4                                             C         11.0       Anionic    2                                                                  Non-Ionic   7.5                                          ______________________________________                                    

The results were as follows:

    ______________________________________                                                       Devel-  Mode of Time of                                                                              Plate                                   Plate                                                                              Resin     oper    Processing                                                                            Dev.   Appearance                              ______________________________________                                        I    Example 4 A       Machine 30     Clean                                   II   Resin A   A       Machine 30     V heavy                                                                       blue stain                              III  Example 4 B       Hand    30     Clean                                   IV   Resin A   B       Hand    90     V heavy                                                                       blue stain &                                                                  scumming                                V    Example 4 C       Machine 30     Clean                                   VI   Resin A   C       Machine 30     Clean                                   ______________________________________                                    

The results illustrate the significant improvement in compatibility withneutral developers afforded by the polysulphonate resin relative toResin A.

Plates I, V and VI were imaged at an exposure of 400 mJcm⁻² and fittedto a web offset litho printing press. Plate VI gave 105,000 impressionsbefore becoming unnacceptable, due to wear. Plates I and V provided over140,000 copies before showing a similar degree of wear.

EXAMPLE 39

An extended machine development trial was undertaken with Plates I andVI of Example 38 with Developers A and C, respectively, using a platethroughput rate of 5 m² per day.

The results were as follows:

    ______________________________________                                                         After 10 days                                                                           Developer                                                                              Plate                                     Plate Developer  Initial pH                                                                              pH       Appearance                                ______________________________________                                        I     A           7.5      7.2      Clean                                     VI    C          11.0      9.3      Heavy blue                                                                    stain/scum                                ______________________________________                                    

The reduction in pH for Developer C during the trial, which isattributable to absorption of carbon dioxide from the atmosphere,resulted in inadequate development of Plate VI after 10 days. DeveloperA showed minimal pH change over this period and gave effectivedevelopment of Plate I throughout the trial.

EXAMPLE 40

A radiation sensitive coating was prepared as follows:

4 Parts by weight of the polysulphonate of Example 3 were dispersed in220 parts by weight of ethylene glycol monomethyl ether. 0.008 Parts byweight of benzyldimethyltetradecyl ammonium chloride were added to thedispersion, which after stirring for 30 minutes, formed a clear solutionof the polysulphonate.

2 Parts by weight of diazo compound 41 described in EP-A 0 030 862 and

0.2 parts by weight of Victoria Blue B were added to this solution.

The resultant coating was used to prepare a radiation sensitive plate asdescribed in Example 31. On Berkey Ascor frame exposure to 400 mJcm⁻²and processing in Developer B of Example 38, the performance of thisplate was identical in all aspects to a plate corresponding to Plate IIIof Example 38.

EXAMPLE 41

The procedure described in Example 40 was repeated, varying theproportion and type of cation-exchange agent employed. The results wereas follows.

    __________________________________________________________________________                          Plate Performance                                       Cations               Development                                                                          Image                                            Examples                                                                           I        II Ratio I:II                                                                         Speed/s                                                                              Oleophilicity                                                                        Step-Wedge                                __________________________________________________________________________    41A  benzyldimethyl-                                                                        H+ 85:15                                                                              15-30  Excellent                                                                            4, 10                                          tetradecyl                                                                    ammonium                                                                 41B  benzyldimethyl-                                                                        H+ 75:25                                                                              15-30  Excellent                                                                            4, 11                                          tetradecyl                                                                    ammonium                                                                 41C  benzyldimethyl-                                                                        -  100:0                                                                              15-30  Excellent                                                                            4, 10                                          hexadecyl                                                                     ammonium                                                                 41D  benzyltriethyl                                                                         H+ 75:25                                                                              15-30  Excellent                                                                            4, 10                                          ammonium                                                                 41E  benzyltriethyl                                                                         -  100:0                                                                              15-30  Excellent                                                                            5, 10                                          ammonium                                                                 41F  trimethyl-                                                                             H+ 85:15                                                                              15-30  Excellent                                                                            4, 10                                          ammonium                                                                      ethylmethacrylate                                                        41G  triethylammonium                                                                       -  100:0                                                                              15-30  Excellent                                                                            4, 10                                          ethylmethacrylate                                                        41H  glycidyltrimethyl                                                                      H+ 85:15                                                                              30     Excellent                                                                            5, 11                                          ammonium                                                                 41I  glycidyltrimethyl                                                                      -  100:0                                                                              15-30  Excellent                                                                            4, 11                                          ammonium                                                                 41J  methyltriphenyl                                                                        H+ 85:15                                                                              15-20  Good   3, 10                                          phosphonium                                                              41K  acetonyltriphenyl                                                                      H+ 85:15                                                                              15-30  Excellent                                                                            4, 10                                          phosphonium                                                              41L  acetonyltriphenyl                                                                      -  100:0                                                                              15-30  Excellent                                                                            4, 10                                          phosphonium                                                              41M  Basic Violet 11.1                                                                      -  100:0                                                                              30     Good   3, 10                                     41N  Basic Blue 7                                                                           -  100:0                                                                              30     Excellent                                                                            4, 11                                     41P  benzyldimethyl-                                                                        Basic                                                                            25:75                                                                              30     Excellent                                                                            4, 11                                          tetradecyl                                                                             Blue 7                                                               ammonium                                                                 __________________________________________________________________________

EXAMPLE 42

Radiation sensitive plates were prepared as described in Example 31using the polysulphonates detailed below. After exposure to 400 mJcm⁻²on a Berkey Ascor Frame and processing, the plates were found to givesimilar excellent development, speed and image oleophilicity to PlateIII of Example 38.

    ______________________________________                                                   Polysulphonates                                                    ______________________________________                                                   Example 5                                                                     Example 6                                                                     Example 7                                                                     Example 8                                                                     Example 9                                                                     Example 10                                                                    Example 11                                                                    Example 19                                                                    Example 20                                                                    Example 22                                                         ______________________________________                                    

EXAMPLE 43

Plates were prepared and processed according to the procedure describedin Example 31, using the following polysulphonates:

    ______________________________________                                                    Example 25                                                                    Example 26                                                                    Example 28                                                        ______________________________________                                    

The resultant plates exhibited very similar characteristics to Plate Aof Example 31.

EXAMPLE 44

Example 34 was repeated using the polysulphonates of Examples 14 and 15individually and in each case omitting the Basic Red 1 shading dye fromthe formulation. After exposure and development these polysulphonatesprovided plates with intense magenta and greenish-blue coloured images,respectively. Image areas exhibited minimal dye leaching on extendeddevelopment and excellent hydrophobicity.

EXAMPLE 45

The polysulphonate of Example 18, and as reference, the unmodifiedcresol novolak of Example 18, were each used to prepare a positiveworking radiation sensitive plate of coating weight 2.0gm⁻² on grainedand anodised aluminium using the following formulation in 95/5methylethyl ketone/ethylene glycol monomethyl ether.

    ______________________________________                                                            Parts by Weight                                           ______________________________________                                        Phenolic Resin        6                                                       5-Sulpho-1,2-naphthoquinone diazide                                                                 1.5                                                     ester                                                                         Sudan Yellow Dye      0.1                                                     ______________________________________                                    

The resultant plates were exposed as in Example 31 and processed inaqueous developers containing non-ionic surfactant as indicated below.

    ______________________________________                                                     Exposure/                                                        Resin        mJmcm.sup.-2                                                                            Developer   Result                                     ______________________________________                                        Example 18   300       pH 13       Clean, 2, 6                                Cresol Novolak                                                                             300       pH 13       Clean, 2, 6                                Example 18   600       pH 10.5     Clean, 2, 7                                Cresol Novolak                                                                             600       pH 10.5     Scum                                       ______________________________________                                    

The results clearly illustrate the improved developability of thepolysulphonate compound over the unmodified cresol novolak in reduced pHdevelopers.

EXAMPLE 46

A solution in methyl ethyl ketone comprising:

3 parts by weight of the dimethacrylate ester of diglycidyl ether ofbisphenol A.,

1 part by weight of the polymer of Example 1

0.15 parts by weight of2(4'-chlorophenyl)-4,6-bis(trichloromethyl)-S-triazine, and

0.15 parts by weight of ethyl Michler's Ketone

was whirler coated onto a sheet of electrochemically grained andanodised aluminium and dried to form a radiation sensitive plate. Thecoating weight was 1.0 gm⁻².

The dried coating was overcoated with poly (vinyl alcohol) to preventoxygen inhibition.

The plate was exposed through a continuous tone Stouffer stepwedge to UVlight (20 mJcm⁻² from a Berkey-Ascor printing down frame) and developedwith an aqueous solution containing sodium propanoate, sodium benzoateand a surfactant. The developed image of the printing plate exhibitedexcellent ink receptivity. When placed on a proofing press, the imagebecame fully charged with ink after 4 passes of the inking rollers. Thestepwedge reading was solid 4, tail 10.

A similar plate which contained the aforementioned phthalic anhydridemodified binder of Example 31 plate in place of the polysulphonatepolymer of Example 1 required 10 passes on the proofing press for theimage to become fully charged with ink. Each plate gave greater than300,000 good copies when run on a web offset press.

EXAMPLE 47

Example 46 was repeated using in place of the polysulphonate of Example1, the polysulphonate of Example 4 (Plate I), and, as a reference, ResinA of Example 38 (Plate II). The development characteristics of theresultant plates were compared using the following developers:

    ______________________________________                                                    Developer Composition                                             Developer pH      Solvent (%)   Surfactant (%)                                ______________________________________                                        (described in                                                                 Example 38)                                                                   D         13      0             Non-ionic (5)                                                                 Anoinic (5)                                   E         10.5    Benzylalcohol (7)                                                                           Anionic (5)                                   ______________________________________                                    

The results were as follows:

    ______________________________________                                                          Time of                                                                       Development/  Plate                                         Plate   Developer min           Appearance                                    ______________________________________                                        I       C         2             Clean                                         II      C         2             Coating                                                                       almost                                                                        totally                                                                       intact                                        I       D           0.5         Clean                                         II      D         1             Minimal                                                                       coating removal                               I       E         1             Clean                                         II      E         2             Very heavy                                                                    stain/scum                                    ______________________________________                                    

EXAMPLE 48

Example 47 was repeated using the same polysulphonate and referenceresins but at an increased level of 3 parts by weight. The plates wereexposed to 50 mJcm⁻² and processed in Developer D of Example 47. Theplate derived from comparison resin A gave no detectable developmentwhilst the polysulphonate derived plate gave a clean plate after a 2minute development period.

EXAMPLE 49

The procedure described in Example 46 was repeated except that 0.10parts by weight of Sudan Yellow were included in the coatingformulations. The plate derived from the polysulphonate of Example 1 wasbright yellow in appearance. The plate derived from the phthalicanhydride derived reference resin was bright orange in colour,indicating premature triggering of the acid-sensitive dye had occurred,and on exposure this plate also exhibited inferior colour contrast tothat of the plate derived from the polysulphonate resin.

EXAMPLE 50

A solution in 1:1 methyl ethyl ketone/ethylene glycol monomethyl ethercomprising:

4 parts by weight of the urethane acrylate disclosed as Prepolymer A inExample 1 of U.S. patent application Ser. No. 07-96893,

1 part by weight of polysulphonate compound, and

0.15 parts by weight of2-(4'-trichloromethylphenacylidene)-1,3,3-trimethyl-5-chloroindoline

was used with a range of polysulphonates detailed below to prepareplates according to the procedure described in Example 46. Afterexposure to 25 mJcm⁻² on a Berkey Ascor frame and processing inDeveloper C of Example 47 the following results were obtained:

    ______________________________________                                              Polysulphonate                                                                            Dev. Time/                                                  Plate Example No  seconds    Oleophilicity                                                                          Wedge                                   ______________________________________                                        1      8          45         Excellent                                                                              5, 12                                   2      9          60         Excellent                                                                              5, 13                                   3     10          45         Excellent                                                                              6, 13                                   4     17          75         Good     4, 12                                   5     21          75         Excellent                                                                              5, 12                                   6     23          60         Excellent                                                                              5, 11                                   7     24          45         Good     4, 11                                   8     29          45         Good     4, 12                                   9     30          60         Good     5, 13                                   ______________________________________                                    

EXAMPLE 51

A solution in methyl ethyl ketone comprising:

3 Parts by weight of the urethane acrylate of Example 50,

1 part by weight of the polysulphonate of Example 12

was used to prepare a radiation sensitive plate (Plate A) as describedin Example 46. A reference plate (Plate B) was also prepared using aphthalic acid modified poly (vinyl butyral) of acid-value 38.9 (Resin B)in place of the polysulphonate.

The plates were exposed on a Berkey Ascor frame (200mJcm-2) andprocessed through Developer D of Example 47. Plate A gave a strongoleophilic image and a wedge of 4,9 illustrating the action of thecounter ion of the polymer as a photoinitiator. Plate B gave no image.Plate B was also exposed to 1000mJcm⁻² but failed to give an image.

EXAMPLE 52

Plates were prepared as described in Example 46 using the polysulphonateof Example 13 (Plate A) and, as a reference, using Resin B described inExample 51 (Plate B), except that in each case ethyl Michler's ketonewas omitted.

The plates were exposed with light of wavelength 435 nm (filtered HgPhotopolymer light source) (60 mJcm⁻²) and processed with Developer D ofExample 47. Plate A gave a strong, olephilic image and a stepwedgereading of 3,8. Plate B failed to give an image with exposures up to1000 mJcm⁻².

Plate A was also exposed to 25 mJcm⁻² with an argon-ion laser operatingat 488nm using an Eocom `Laserite` exposure unit. A similar strong imageto that described above was produced after processing in Developer D.This example illustrates the photo-sensitising action of thepolysulphonate resin.

EXAMPLE 53

A solution in 1-methoxy-2-propanol comprising:

3 Parts by weight of the urethane acrylate of Example 50,

1 part by weight of the polysulphonate of Example 4,

0.15 parts by weight of2-(4'trichloromethylphenacylidene)-1,3,3-trimethyl-5-chloroindoline, 0.5parts by weight of the diazo resin described in Example 31, and 0.1parts by weight of

Sudan Yellow

was used to prepare radiation sensitive plates as described in Example46, except that overcoating with poly (vinyl alcohol) was omitted. Theplate was exposed on a Berkey Ascor frame to 200 mJcm⁻². On processingin Developer C of Example 38, rapid development occurred to provide ahighly oleophilic image and a step wedge reading of 5,9.

EXAMPLE 54

An aqueous coating solution containing:

2 Parts by weight of the zinc chloride salt of 4-diazodiphenylamine-formaldehyde condensate and

1 part by weight of the polysulphonate of Example 16

was applied to grained and anodised aluminium to provide aradiation-sensitive plate of coating weight 0.3gm⁻². After exposure to100mJcm⁻², the plate was processed with the aqueous emulsion developerdescribed in Example 1 of U.S. Pat No. 4,714,670 to provide a distinctred image and a stepwedge reading of 5,10.

EXAMPLE 55

Example 54 was repeated except that the polysulphonate of Example 3 wasused to make two plates as follows: The resin was dispersed in water and

i) ammonium hydroxide (Plate A) and

ii) 2-amino-2-methyl-1-propanol (Plate B) were added dropwise untildissolution of the polysulphonate occurred. An aqueous solution of thediazo resin was added to each polymer solution and these were used tomake plates of coating weight 0.2gm⁻². Exposure, processing and resultswere similar to those described in Example 54.

EXAMPLE 56

32% parts by weight of Diazo R0220, (a novolak resin partly esterifiedwith 2,1-naphthoquinone diazide-5-sulphonic acid and available throughRohner Ltd.) was dissolved in 300 parts by weight of THF at roomtemperature. To this stirred solution was added 0.5 parts by weightpyridine and 0.1 parts by weight 4-dimethylaminopyridine followed by 13parts by weight 2-sulphobenzoic acid cyclic anhydride. Gentle coolingwas applied as necessary to keep the temperature at 15° C. to 25° C. andthe reaction was left stirring for a total of six hours. The product wasisolated as a pale brown solid by drowning out the reaction solutioninto 3000 parts by weight water containing 1% v/v concentratedhydrochloric acid. The product was filtered and washed twice in waterbefore drying at 30° C. under vacuum. 35 parts by weight of material wasobtained having an AV of 27 and less than 0.2% w/w of free2-sulphobenzoic acid.

20 parts by weight of the polysulphonate obtained above was dissolved in200 parts by weight of THF, to which solution 5 parts by weight ofbenzyldimethyltetradecylammonium chloride was added. The resultingsolution was then sprayed into 3000 parts by weight of vigorouslyagitated water and the precipitated solid was filtered off, washedseveral times in water and dried under vacuum at 30° C. to constantweight to yield 23 parts by weight of pale brown solid. Analysis showedpolymer bound counterion to be 12.3% w/w and free counterion to be lessthan 0.1% w/w

We claim:
 1. A radiation sensitive composition comprising an admixtureof:(i) a polymeric material comprising a plurality of substituentsulphonate groups wherein the polymeric material is derived from apolymer having a plurality of pendant hydroxy groups attached to thepolymer backbone, or a side chain thereof, and wherein the sulphonategroups are selected from groups of the general formula: ##STR6## where Xis an aliphatic, aromatic, carbocyclic or heterocyclic group; Y ishydrogen, halogen, or an alkyl, aryl, alkoxy, aryloxy or aralkyl group,CO₂ Z⁺, CO₂ R or SO₃ Z⁺ ; Z⁺ is a cationic counter-ion, R is hydrogen,alkyl, alkylene, aryl or aralkyl group and O is derived from a hydroxylgroup of the polymer, less H and (ii) one member selected from the groupconsisting of diazo compounds, photopolymerizable compounds and positiveworking photo solubilisable compounds.
 2. A composition according toclaim 1 wherein the polymeric material comprises from 5% to 95% byweight of the radiation sensitive composition.
 3. A compositionaccording to claim 1 wherein the sulphonate groups are derived fromsulphonato substituted acids of the formula ##STR7## where X, Y, Z⁺ andR have the meanings specified in claim
 1. 4. A composition according toclaim 1 wherein the sulphonate groups are derived from a reactivederivative of a carboxylic or sulphonic acid.
 5. A composition accordingto claim 4 wherein the reactive derivative of the carboxylic orsulphonic acid is an anhydride or acid chloride.
 6. A compositionaccording to claim 1 wherein the molecular weight of the said polymericmaterial is in the range of 900 to 200,000.
 7. A composition accordingto claim 1 wherein the acid value or acid value equivalence of the saidpolymeric material is in the range of 5 to
 150. 8. A compositionaccording to claim 1 wherein the said polymeric material comprises twoor more different counter-ion species.
 9. A composition according toclaim 8 wherein at least one of the counter-ion species is radiationsensitive.